This place begun as a Vicus and grew into a town, The town walls are shown in brown, the yellow lines are the fort.
http://roman-britain.co.uk/places/godmanchester.htm
http://www.godmanchester.net/history/roman%20mansio.htm
http://www.godmanchester.co.uk/roman-duroviutum
http://www2.rgzm.de/transformation/unitedkingdom/smalltowns/Img46.htm